Preparation Of Single Pt/Ir Atom Catalyst And Study On Its Performance Of Hydrogen Evolution Reaction

The energy crisis and environmental pollution have caused widespread concern and research on sustainable green energy with the development of economy.Hydrogen energy is an excellent representative of sustainable green energy due to its high combustion heat,water as the combustion product,and easy storage and transportation.Scientific research in the field of hydrogen energy is gradually increasing.Hydrogen evolution reaction which is a sustainable and green way of production can produce hydrogen.The catalyst for the hydrogen evolution reaction（HER）can improve the production efficiency of hydrogen,reduce the loss of electric energy and reduce the production cost because the activation energy of HER can be decreased when it uses.The design and engineering of efficient electrocatalysts for the hydrogen evolution reaction are critical for the development of renewable energy conversion and storage.At present,the best catalysts for hydrogen evolution reaction are some noble metal catalysts,such as platinum（Pt）and iridium（Ir）.However,due to the high cost of these precious metal catalysts and their scarcity on the earth,they are not suitable for large-scale use.In recent years,more and more work has been done in the field of single-atom catalysis,and the field of single-atom catalysis has attracted widespread attention.Single-atom electrocatalysts（SACs）which is a new achievement in the field of catalysis can achieve almost 100%atomic utilization and high catalytic activity in catalytic reactions,thereby minimizing the use of precious metals.In this thesis,I prepared Pt single-atom catalysts and Irsingle-atom catalysts by a one-step synthetic co-precipitation method,and performed structural characterization and electrochemical performance tests on these two single-atom catalysts.1.A catalyst for hydrogen evolution reaction with Pt single atoms supported on graphene-modified titania nanosheets（Pt@TiO₂/NSG）was successfully prepared.The results of X-ray photoelectron spectroscopy（XPS）and high-angle annular dark-field scanning transmission electron microscope（HAADF-STEM）show that Pt is dispersed at the single atomic level on the TiO₂/NSG structure and is anchored by a large number of surface functional groups（such as O）on the heavily exposed basal planes in the TiO₂/NSG heterostructure.There is a strong electronic interaction between the active center Pt atoms and the TiO₂/NSG substrate,and the synergistic effect of the two enables the Pt@TiO₂/NSG electrocatalyst to exhibit excellent electrocatalytic activity for HER in acidic electrolytes.At a current density of-10 mA cm^-2,the overpotential value is-38 mV,with a small Tafel slope of 40mV/dec,and the overpotential value of the HER polarization curve after the1000th cycle is only with an offset of 1 mV.When these values compare to the commercial 20 wt%Pt/C catalyst,they are better than them.2.A catalyst for hydrogen evolution reaction with Irsingle atoms supported on graphene-modified titania nanosheets（Ir@TiO₂/NSG）was successfully prepared by the same strategy.It was observed that the Ir@TiO₂/NSG catalyst had a multi-layer structure with good planar ductility by scanning electron microscope（SEM）.Through the analysis of XPS and HAADF-STEM results,it can be seen that the dispersion of Irat the single atomic level is successfully realized,and most of the dispersed single atoms are located on the lattice,and a small part is located in the gaps of the crystal plane.The stability of the catalyst has been proved.In the electrochemical performance test,the hydrogen evolution overpotential value of the Ir@TiO₂/NSG catalyst is 64 mV.The commercial 20 wt%Pt/C catalyst^￠s overpotential value is 45 mV so the catalytic performance of the two is comparable.The Tafel slope value of the Ir@TiO₂/NSG catalyst is 35 mV/dec,which is lower than the commercial Pt/C catalyst（48 mV/dec）,indicating that the Ir@TiO₂/NSG catalyst has better hydrogen evolution kinetics.The overpotential value of the LSV curve of the Ir@TiO₂/NSG catalyst increased by only 2 mV after 1000 cyclic voltammetry scans,which indicates the superior stability of the Ir@TiO₂/NSG catalyst.The successful preparation of two single-atom catalysts reflects the reproducibility of the experimental scheme in this paper.This work provides a new strategy for the controllable development of Pt/IrSACs with high activity,low cost,and long-term stability.